WORKING IN
HOT ENVIRONMENTS
Reprinted 1992, with Minor Changes
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Centers for Disease Control
National Institute for Occupational Safety and Health
April 1986
DISCLAIMER
Mention of the name of any company or product does not constitute
endorsement by the National Institute for Occupational Safety
and Health (NIOSH).
The purpose of this revised pamphlet is to provide employers
and workers with an overview of the health hazards associated
with work in hot environments, and to alert them to the
precautions which should be taken to prevent injuries and other
health problems due to heat stress.
The information contained in this publication is in the public
domain and may be reproduced without further request. Appropriate
source citation, while not required, would be appreciated.
ADDITIONAL COPIES OF THIS PAMPHLET ARE AVAILABLE FROM:
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Cincinnati, Ohio 45226
FAX (513) 5338573
DHHS (NIOSH) Publication No. 86-112
This publication is a revision of the 1980 pamphlet entitled
"Hot Environments, " formerly DHHS(NIOSH) Publication
No. 80132.
CONTENTS
Page
3 -- Heat Stroke
4 -- Heat Exhaustion
5 -- Heat Cramps
5 -- Fainting
6 -- Heat Rash
6 -- Transient Heat Fatigue
8 -- Number and Duration of Exposures
8 -- Thermal Conditions in the Workplace
9 -- Rest Areas
9 -- Drinking Water
10--Protective Clothing
- From iron workers to pastry bakers, Americans
work in a wide variety of hot or hot and humid environments:
- Outdoor operations in hot weather, including
surface mining, roofing, road repair and construction, dam building,
and other construction
- Farming operations
- Iron, steel and nonferrous foundries
- Brick-firing and ceramics operations
- Glass products manufacturing plants
- Rubber products manufacturing plants
- Electrical utilities (particularly boiler rooms)
- Bakeries
- Confectioneries
- Restaurant kitchens
- Laundries
- Food canneries
- Mines
- Smelters
- Steam tunnels
- Being uncomfortable is not the major problem
with working in high temperatures and humidities. Workers who
are suddenly exposed to working in a hot environment face additional
and generally avoidable hazards to their safety and health. The
employer should provide detailed instructions on preventive measures
and adequate protection necessary to prevent heat stress.
The human body, being warm blooded, maintains a fairly constant
internal temperature, even though it is being exposed to varying
environmental temperatures. To keep internal body temperatures
within safe limits, the body must get rid of its excess heat,
primarily through varying the rate and amount of blood circulation
through the skin and the release of fluid onto the skin by the
sweat glands. These automatic responses usually occur when the
temperature of the blood exceeds 98.6oF and are kept in balance
and controlled by the brain. In this process of lowering internal
body temperature, the heart begins to pump more blood, blood vessels
expand to accommodate the increased flow, and the microscopic
blood vessels (capillaries) which thread through the upper layers
of the skin begin to fill with blood. The blood circulates closer
to the surface of the skin, and the excess heat is lost to the
cooler environment.
If heat loss from increased blood circulation through the
skin is not adequate, the brain continues to sense overheating
and signals the sweat glands in the skin to shed large quantities
of sweat onto the skin surface. Evaporation of sweat cools the
skin, eliminating large quantities of heat from the body.
As environmental temperatures approach normal skin temperature,
cooling of the body becomes more difficult. If air temperature
is as warm as or warmer than the skin, blood brought to the body
surface cannot lose its heat. Under these conditions, the heart
continues to pump blood to the body surface, the sweat glands
pour liquids containing electrolytes onto the surface of the skin
and the evaporation of the sweat becomes the principal effective
means of maintaining a constant body temperature. Sweating does
not cool the body unless the moisture is removed from the skin
by evaporation. Under conditions of high humidity, the evaporation
of sweat from the skin is decreased and the body's efforts to
maintain an acceptable body temperature may be significantly impaired.
These conditions adversely affect an individual's ability to work
in the hot environment. With so much blood going to the external
surface of the body, relatively less goes to the active muscles,
the brain, and other internal organs; strength declines; and fatigue
occurs sooner than it would otherwise. Alertness and mental capacity
also may be affected. Workers who must perform delicate or detailed
work may find their accuracy suffering, and others may find their
comprehension and retention of information lowered.
Certain safety problems are common to hot environments. Heat
tends to promote accidents due to the slipperiness of sweaty palms,
dizziness, or the fogging of safety glasses. Wherever there exists
molten metal hot surfaces, steam, etc., the possibility of burns
from accidental contact also exists.
Aside from these obvious dangers, the frequency of accidents,
in general appears to be higher in hot environments than in more
moderate environmental conditions. One reason is that working
in a hot environment lowers the mental alertness and physical
performance of an individual. Increased body temperature and physical
discomfort promote irritability, anger, and other emotional states
which sometimes cause workers to overlook safety procedures or
to divert attention from hazardous tasks.
Excessive exposure to a hot work environment can bring about
a variety of heat-induced disorders.
Heat Stroke
Heat stroke is the most serious of health problems associated
with working in hot environments. It occurs when the body's temperature
regulatory system fails and sweating becomes inadequate. The body's
only effective means of removing excess heat is compromised with
little warning to the victim that a crisis stage has been reached.
A heat stroke victim's skin is hot, usually dry, red or spotted.
Body temperature is usually 105oF or higher, and the victim is
mentally confused, delirious, perhaps in convulsions, or unconscious.
Unless the victim receives quick and appropriate treatment, death
can occur.
Any person with signs or symptoms of heat stroke requires
immediate hospitalization. However, first aid should be immediately
administered. This includes removing the victim to a cool area,
thoroughly soaking the clothing with water, and vigorously fanning
the body to increase cooling. Further treatment at a medical facility
should be directed to the continuation of the cooling process
and the monitoring of complications which often accompany the
heat stroke. Early recognition and treatment of heat stroke are
the only means of preventing permanent brain damage or death.
Heat Exhaustion
Heat exhaustion includes several clinical disorders having
symptoms which may resemble the early symptoms of heat stroke.
Heat exhaustion is caused by the loss of large amounts of fluid
by sweating, sometimes with excessive loss of salt. A worker suffering
from heat exhaustion still sweats but experiences extreme weakness
or fatigue, giddiness, nausea, or headache. In more serious cases,
the victim may vomit or lose consciousness. The skin is clammy
and moist, the complexion is pale or flushed, and the body temperature
is normal or only slightly elevated.
In most cases, treatment involves having the victim rest in
a cool place and drink plenty of liquids. Victims with mild cases
of heat exhaustion usually recover spontaneously with this treatment.
Those with severe cases may require extended care for several
days. There are no known permanent effects.
CAUTION
Persons with heart problems or those on a low sodium
diet who work in hot environments should consult a physician
about what to do under these conditions.
Heat Cramps
Heat cramps are painful spasms of the muscles that occur among
those who sweat profusely in heat, drink large quantities of water,
but do not adequately replace the body's salt loss. The drinking
of large quantities of water tends to dilute the body's fluids,
while the body continues to lose salt. Shortly thereafter, the
low salt level in the muscles causes painful cramps. The affected
muscles may be part of the arms, legs, or abdomen, but tired muscles
(those used in performing the work) are usually the ones most
susceptible to cramps. Cramps may occur during or after work hours
and may be relived by taking salted liquids by mouth.
CAUTION
Persons with heart problems or those on a low low
sodium diet who work in hot environments should consult a
physician about what to do under these conditions.
Fainting
A worker who is not accustomed to hot environments and who
stands erect and immobile in the heat may faint. With enlarged
blood vessels in the skin and in the lower part of the body due
to the body's attempts to control internal temperature, blood
may pool there rather than return to the heart to be pumped to
the brain. Upon lying down, the worker should soon recover. By
moving around, and thereby preventing blood from pooling, the
patient can prevent further fainting.
Heat Rash
Heat rash, also known as prickly heat, is likely to occur
in hot, humid environments where sweat is not easily removed from
the surface of the skin by evaporation and the skin remains wet
most of the time. The sweat ducts become plugged, and a skin rash
soon appears. When the rash is extensive or when it is complicated
by infection, prickly heat can be very uncomfortable and may reduce
a worker's performance. The worker can prevent this condition
by resting in a cool place part of each day and by regularly bathing
and drying the skin.
Transient Heat Fatigue
Transient heat fatigue refers to the temporary state of discomfort
and mental or psychologic strain arising from prolonged heat exposure.
Workers unaccustomed to the heat are particularly susceptible
and can suffer, to varying degrees, a decline in task performance,
coordination, alertness, and vigilance. The severity of transient
heat fatigue will be lessened by a period of gradual adjustment
to the hot environment (heat acclimatization).
One of the best ways to reduce heat stress on workers is to
minimize heat in the workplace. However, there are some work environments
where heat production is difficult to control, such as when furnaces
or sources of steam or water are present in the work area or when
the workplace itself is outdoors and exposed to varying warm weather
conditions.
Humans are, to a large extent, capable of adjusting to the
heat. This adjustment to heat, under normal circumstances, usually
takes about 5 to 7 days, during which time the body will undergo
a series of changes that will make continued exposure to heat
more endurable.
On the first day of work in a hot environment, the body temperature,
pulse rate, and general discomfort will be higher. With each succeeding
daily exposure, all of these responses will gradually decrease,
while the sweat rate will increase. When the body becomes acclimated
to the heat, the worker will find it possible to perform work
with less strain and distress.
Gradual exposure to heat gives the body time to become accustomed
to higher environmental temperatures. Heat disorders in general
are more likely to occur among workers who have not been given
time to adjust to working in the heat or among workers who have
been away from hot environments and who have gotten accustomed
to lower temperatures. Hot weather conditions of the summer are
likely to affect the worker who is not acclimatized to heat. Likewise,
workers who return to work after a leisurely vacation or extended
illness may be affected by the heat in the work environment. Whenever
such circumstances occur, the worker should be gradually reacclimatized
to the hot environment.
Many industries have attempted to reduce the hazards of heat
stress by introducing engineering controls, training workers in
the recognition and prevention of heat stress, and implementing
work-rest cycles. Heat stress depends, in part, on the amount
of heat the worker's body produces while a job is being performed.
The amount of heat produced during hard, steady work is much higher
than that produced during intermittent or light work. Therefore,
one way of reducing the potential for heat stress is to make the
job easier or lessen its duration by providing adequate rest time.
Mechanization of work procedures can often make it possible to
isolate workers from the heat sources (perhaps in an air-conditioned
booth) and increase overall productivity by decreasing the time
needed for rest. Another approach to reducing the level of heat
stress is the use of engineering controls which include ventilation
and heat shielding.
Number and Duration of Exposures
Rather than be exposed to heat for extended periods of time
during the course of a job, workers should, wherever possible,
be permitted to distribute the workload evenly over the day and
incorporate work-rest cycles. Work-rest cycles give the body an
opportunity to get rid of excess heat, slow down the production
of internal body heat, and provide greater blood flow to the skin.
Workers employed outdoors are especially subject to weather
changes. A hot spell or a rise in humidity can create overly stressful
conditions. The following practices can help to reduce heat stress:
- Postponement of nonessential tasks,
- Permit only those workers acclimatized to heat to perform
the more strenuous tasks, or
- Provide additional workers to perform the tasks keeping in
mind that all workers should have the physical capacity to perform
the task and that they should be accustomed to the heat.
Thermal Conditions in the Workplace
A variety of engineering controls can be introduced to minimize
exposure to heat. For instance, improving the insulation on a
furnace wall can reduce its surface temperature and the temperature
of the area around it. In a laundry room, exhaust hoods installed
over those sources releasing moisture will lower the humidity
in the work area. In general the simplest and least expensive
methods of reducing heat and humidity can be accomplished by:
- Opening windows in hot work areas,
- Using fans, or
- Using other methods of creating airflow such as exhaust ventilation
or air blowers.
Rest Areas
Providing cool rest areas in hot work environments considerably
reduces the stress of working in those environments. There is
no conclusive information available on the ideal temperature for
a rest area. However, a rest area with a temperature near 76/F
appears to be adequate and may even feel chilly to a hot, sweating
worker, until acclimated to the cooler environment. The rest area
should be as close to the workplace as possible. Individual work
periods should not be lengthened in favor of prolonged rest periods.
Shorter but frequent work-rest cycles are the greatest benefit
to the worker.
Drinking Water
In the course of a day's work in the heat, a worker may
produce as much as 2 to 3 gallons of sweat. Because so many heat
disorders involve excessive dehydration of the body, it is essential
that water intake during the workday be about equal to the amount
of sweat produced. Most workers exposed to hot conditions drink
less fluids than needed because of an insufficient thirst drive.
A worker, therefore, should not depend on thirst to signal when
and how much to drink. Instead, the worker should drink 5 to 7
ounces of fluids every 15 to 20 minutes to replenish the necessary
fluids in the body. There is no optimum temperature of drinking
water, but most people tend not to drink warm or very cold fluids
as readily as they will cool ones. Whatever the temperature of
the water, it must be palatable and readily available to the worker.
Individual drinking cups should be provided--never use a common
drinking cup.
Heat acclimatized workers lose much less salt in their sweat
than do workers who are not adjusted to the heat. The average
American diet contains sufficient salt for acclimatized workers
even when sweat production is high. If, for some reason, salt
replacement is required, the best way to compensate for the loss
is to add a little extra salt to the food. Salt tablets should
not be used.
CAUTION
Persons with heart problems or those on a low sodium
diet who work in hot environments should consult a physician about
what to do under these conditions.
Protective Clothing
Clothing inhibits the transfer of heat between the body and
the surrounding environment. Therefore, in hot jobs where the
air temperature is lower than skin temperature, wearing clothing
reduces the body's ability to lose heat into the air.
When air temperature is higher than skin temperature, clothing
helps to prevent the transfer of heat from the air to the body.
However, this advantage may be nullified if the clothes interfere
with the evaporation of sweat.
In dry climates, adequate evaporation of sweat is seldom a
problem. In a dry work environment with very high air temperatures,
protective clothing could be an advantage to the worker. The proper
type of clothing depends on the specific circumstance. Certain
work in hot environments may require insulated gloves, insulated
suits, reflective clothing, or infrared reflecting face shields.
For extremely hot conditions, thermally conditioned clothing is
available. One such garment carries a self-contained air conditioner
in a backpack, while another is connected a compressed air source
which feeds cool air into the jacket or coveralls through a vortex
tube. Another type of garment is a plastic jacket which has pockets
that can be filled with dry ice or containers of ice.
The key to preventing excessive heat stress is educating the
employer and worker on the hazards of working in heat and the
benefits of implementing proper controls and work practices. The
employer should establish a program designed to acclimatize workers
who must be exposed to hot environments and provide necessary
work-rest cycles and water to minimize heat stress.
During unusually hot weather conditions lasting longer than
2 days, the number of heat illnesses usually increases. This is
due to several factors, such as progressive body fluid deficit,
loss of appetite (and possible salt deficit), buildup of heat
in living and work areas, and breakdown of air-conditioning equipment.
Therefore, it is advisable to make a special effort to adhere
rigorously to the above preventive measures during these extended
hot spells and to avoid any unnecessary or unusual stressful activity.
Sufficient sleep and good nutrition are important for maintaining
a high level of heat tolerance. Workers who may be at a greater
risk of heat illnesses are the obese, the chronically ill, and
older individuals.
When feasible, the most stressful tasks should be performed
during the cooler parts of the day (early morning or at night).
Double shifts and overtime should be avoided whenever possible.
Rest periods should be extended to alleviate the increase in the
body heat load.
The consumption of alcoholic beverages during prolonged periods
of heat can cause additional dehydration. Persons taking certain
medications (e.g., medications for blood pressure control, diuretics,
or water pills) should consult their physicians in order to determine
if any side effects could occur during excessive heat exposure.
Daily fluid intake must be sufficient to prevent significant weight
loss during the workday and over the workweek.
- American Conference of Governmental Industrial
Hygienists [1991]. TLVs. threshold limit values and biological
exposure indices for 1985-86, Cincinnati OH: ACGIH pp. 91-98.
- NIOSH [1986]. Criteria for a recommended standard . . occupational exposure to hot environments - revised criteria.
Cincinnati, OH: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control, National Institute
for Occupational Safety and Health, DHHS(NIOSH) Publication No.
86-113.
- NIOSH [1976]. Standards for occupational exposures
to hot environments--proceedings of symposium. Cincinnati, OH:
U.S. Department of Health, Education and Welfare, Public Health
Service, Center for Disease Control, National Institute for Occupational
Safety and Health, HEW(NIOSH) Publication No. 76-100.
- Westinghouse Electric Corporation [1986]. Heat
stress management program for nuclear power plants. University
Park, PA: Pennsylvania State University, GPU Nuclear Corporation.
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